The present invention relates to a stage movement control apparatus for controlling the position of a stage which is movable along a straight line or in two orthogonal axis directions, and also to a stage movement control method. The present invention further relates to a projection exposure apparatus which includes the above stage movement control apparatus, and also to a projection exposure method carried out by a system including the above stage movement control apparatus.
In a lithography process carried out during the production of semiconductor devices, liquid crystal display devices, etc., a projection exposure apparatus has heretofore been used to project and transfer a circuit pattern formed on a mask onto a photosensitive substrate, e.g. a wafer, a plate, etc., through a projection optical system. There are various types of projection exposure apparatus. In the production of semiconductor devices, however, the step-and-repeat photolithographic system with demagnification, i.e. so-called stepper, has become the leading projection exposure apparatus because the line width of patterns to be formed on a wafer has been reduced with the increasing degree of integration of circuits.
The stepper is designed to expose a wafer by the step-and-repeat method through a projection optical system having an exposure field capable of covering the whole pattern area of one mask (reticle). The stepper is superior in resolution, registration accuracy, etc. to aligners that employ the scanning exposure method, and is therefore considered to be the leading projection exposure apparatus in future.
However, a step-and-scan projection exposure apparatus has recently been proposed as a novel system designed to attain high resolution by improving the scanning exposure system. The step-and-scan projection exposure apparatus is a mixture of a scanning system in which, while a mask (reticle) is being one-dimensionally scanned, a wafer is one-dimensionally scanned at a speed synchronized with the scanning of the mask, and a system in which the wafer is stepwise moved.
Incidentally, projection exposure apparatuses of the above two different types are each provided with a wafer stage (XY-stage) which is movable in two orthogonal axis directions to successively expose shot regions on a wafer. In positioning of the stage, it is decided that the positioning has been completed when an error between a target position of the stage and the present position of the stage, which is obtained as an output value of an interferometer for detecting the position of the stage, has become smaller than a predetermined value. Immediately after the completion of the positioning, exposure is carried out.
However, in the above-described conventional projection exposure apparatuses, vibration of the stage during the exposure process, after the completion of the wafer stage positioning, is not monitored. Therefore, when a pattern image transferred by the exposure is degraded (unsharp), it is difficult to judge whether the degradation of the transferred image is due to the vibration of the stage or other factors. Further, the effect of the stage vibration on the degradation of the transferred image cannot be quantitatively evaluated.
Meanwhile, Japanese Patent Application Unexamined Publication (KOKAI) No. 60-32050 (85/32050) discloses "an exposure apparatus which is provided with at least one means for detecting vibration of a photosensitive material on which an image is projected and formed, so that an amount of displacement between the projected image and the photosensitive material is detected by the detecting means". However, the vibration detecting means mentioned in the invention disclosed in the publication is a sensor for directly detecting vibration of the stage, e.g., an accelerator, a micro-displacement gauge, etc., which is not a member that should inherently be provided in a projection exposure apparatus. Therefore, provision of such a detecting means causes costs to rise correspondingly.
The invention disclosed in the above publication is designed not to detect unsharpness (degradation) of the projected image caused by the vibration of the stage during exposure, but to effect positioning of the stage on the basis of the output of the vibration detecting means and not the output of an interferometer. Accordingly, the disclosed invention also suffers from the problems that, when a pattern image transferred by exposure is degraded (unsharp), it is impossible not only to judge whether the degradation of the transferred image is due to the vibration of the stage or other factors, but also to evaluate quantitatively the effect of the stage vibration on the degradation of the transferred image.
In view of the above-described problems of the prior art, a first object of the present invention is to provide a stage movement control apparatus which is capable of quantitatively evaluating vibration characteristics immediately after the completion of the stage positioning process.
A second object of the present invention is to provide a projection exposure apparatus which is capable of quantitatively evaluating the effect of the stage vibration on the degradation of the transferred image, thereby making it possible to prevent degradation of a pattern image projected and transferred onto a photosensitive substrate.